JPH0115808B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical wavelength meter that separates incident light into two lights and measures the wavelength of the incident light as a ratio of the intensities of the two lights.

Conventionally, the configuration shown in FIG. 1 has been considered as an optical wavelength measuring device. To explain this operation, light emitted from the optical connector 2 attached to the end face of the optical fiber 1 is collimated by the lens 3 and input to the interference film filter 4. This interference film filter 4
is arranged diagonally with respect to the incident light, a part of the incident light is transmitted and enters the light receiver _5a , and the remaining light is reflected and enters the light receiver _5b , where each is converted into an electrical quantity. . The values of these two electric quantities change depending on the wavelength of the incident light due to the filter characteristics of the interference film filter 4.

Next, the logarithmic ratio of these two quantities of electricity is calculated by the calculation circuit 6.
The optical wavelength is indicated on the display section 7 by comparing this logarithmic ratio with the initially stored optical wavelength-logarithmic ratio characteristic.

However, the interference film filter 4 used here is composed of a multilayer dielectric film, and the typical characteristics that can be manufactured at present are shown in FIG. 2. In general, it is desirable that filters used in optical wavelength meters cover a wide band and have characteristics that change linearly. However, the filter shown in Figure 2 can only be used in the wavelength range of 0.8 to 0.9 μm, about 0.1 μm, and even within that wavelength range, the P ₂ /P ₁ logarithmic ratio does not change linearly, so it is difficult to measure. There was a drawback that caused errors. Furthermore, when the interference film filter 4 is used obliquely with respect to the incident light, a large dynamic range of the P ₂ /P ₁ logarithm ratio cannot be obtained, which makes it difficult to increase the resolution.

In order to eliminate these drawbacks, this invention utilizes the fact that the polarization rotation angle of an optical wave plate has wavelength characteristics instead of using an interference film filter, and uses a polarization separation device such as a birefringent element in the rear stage of the wave plate. An element is provided to extract two polarized optical outputs that vary depending on the wavelength.

FIG. 3 shows an embodiment of the present invention, in which a linearly polarized light beam 11 has optical rotation and is incident on an optical wave plate 12 made of, for example, quartz crystal. A polarization separation element 13 such as calcite is located after the optical wavelength plate 12.
are arranged, and the two lights separated by the polarization separation element 13 are incident on the light receiving elements 5 _a and 5 _b , respectively.

In this operation, a linearly polarized light beam 11 undergoes rotation of its plane of polarization by an optical wave plate 12, and is then separated into two orthogonal polarization components by a polarization separation element 13. This behavior is shown in Figure 4. That is, the polarization plane 14 of the light beam 11 is rotated by an angle θ by the wave plate 12 to form a polarization plane 15, which is separated into respective components 15x and 15y of the orthogonal polarization plane by the polarization separation element 13. These two separated orthogonally polarized light beams 15 _x and 15 _y are converted into electrical signals by the light receiving elements 5 _a and 5 _b , respectively. In the subsequent operation of the optical wavelength meter, as shown in Fig. 1, the logarithmic ratio of the powers P ₁ and P ₂ converted into two electrical signals is taken by the arithmetic circuit 6, and the display section is displayed according to this ratio. 7 shows the light wavelength.

The rotation angle θ of the plane of polarization by the optical wave plate 12 is the thickness of the wave plate 12. Varies depending on the wavelength used and temperature.
Of these, the variation in rotation angle due to temperature is extremely small.
There is no problem in using it as an optical wavelength meter. This invention utilizes the fact that the rotation angle θ changes depending on the wavelength used, and by appropriately selecting the thickness of the wave plate 12, it is possible to gradually rotate the plane of polarization over a very wide band. Conversely, it is also possible to rapidly rotate the plane of polarization within a narrow wavelength range. When using quartz crystal as such a wave plate 12, its thickness is set to several μm to several hundred μm.

Therefore, we decided to change the wavelength range measured by the optical wavelength meter to the short wavelength band (0.7 to 1.1 μm) and the long wavelength band (1.0 to 1.7 μm) in accordance with the sensitivity characteristics of the currently developed photodetector.
The characteristics when the polarization separation filter of the present invention is designed into two types are shown in FIGS. 5 and 6, respectively. The two types of curves (broken line and solid line) shown in Figures 5 and 6 are obtained by selecting two types of optical wave plate thicknesses that match the wavelength range used. It utilizes linearity over a wide band, and is suitable for measuring the wavelength of light sources with a wide emission spectrum such as LEDs. On the other hand, the solid line has a wide dynamic range of logarithmic ratio to obtain high resolution, but since the linearity is slightly lost at both ends of the wavelength used, it is suitable for light sources with narrow emission spectrum widths such as LDs. .

Note that, like the conventional optical wavelength meter shown in FIG. 1, the optical wavelength meter of the present invention can also measure the input optical power by taking the sum of P ₁ and P ₂ .

FIG. 7 shows another embodiment of the present invention, in which the first
The same reference numerals are given to the parts corresponding to those in FIG. 2 and FIG. One optical output is incident on the wave plate 12 and the other optical output is applied to the non-reflective termination 30.
It is absorbed by. Further, condensing lenses 21 and 22 are arranged in front of the light receiving elements 5 _a and 5 _b .

This operation is the same as the operation described with reference to FIG. 3, except that the incident light corresponds to the output light from the optical fiber 1. In other words, since the light emitted from the optical fiber 1 generally does not have polarization characteristics,
A polarization separation optical element 10 is provided in front of the optical wave plate 12,
Only one separated linearly polarized light beam is incident on the optical wave plate 12. The subsequent operations are as described above. Further, the remaining polarized light separated by the polarization separation optical element 10 is absorbed by the non-reflection termination 30, so that the reflected light does not have any influence.

FIG. 8 shows still another embodiment of the present invention, in which, in addition to the configuration shown in FIG. 7, a light receiving element 16 is added in place of the non-reflection termination 30, and a condensing lens 23 is added in front of the light receiving element 16. The remaining polarized light beam separated by the polarization separation element 10 is received by the light receiving element 16, and its optical power is
Convert P ₃ into an electrical signal. This is because conventional optical wavelength meters were configured to be able to measure optical power, so it is now possible to measure the optical power of unpolarized or polarized light, such as the light emitted from optical fiber 1. Therefore, P ₃ can be added to the sum of P ₁ and P ₂ .

Furthermore, since the polarization separation element and the optical wavelength plate used in these examples can be realized in an extremely small size, the size of the entire filter can be constructed within a few square centimeters.

As explained above, the optical wavelength meter according to the present invention covers a very wide band, can linearly obtain the logarithmic ratio of two polarization-separated lights over a wide dynamic range, and can be constructed in a small size. It has features of high precision and ease of use.

[Brief explanation of drawings]

Figure 1 shows the configuration of a conventional optical wavelength meter, Figure 2 shows the configuration of a conventional optical wavelength meter.
The figure is a characteristic diagram of the interference film filter used in Figure 1, Figure 3 is a diagram showing the configuration of an embodiment of this invention, Figure 4 is an explanatory diagram of the operating principle of Figure 3, and Figure 5 and FIG. 6 are characteristic diagrams of the filter of the present invention, and FIGS. 7 and 8 are diagrams showing the configuration of other embodiments of the present invention, respectively. 1: Optical fiber, 2: Optical connector, 3: Collimating lens, 4: Interference film filter, 5a, _5b :
Light receiving element, 6: Logarithmic ratio processing calculation circuit, 7: Display circuit, 10, 13: Polarization separation optical element, 11: Incident light beam, 12: Optical wavelength plate, 21, 22, 23: Condensing lens, 30 : Non-reflective termination.

Claims (1)

[Claims] 1. An optical wave plate that receives linearly polarized incident light and whose polarization rotation angle has wavelength characteristics, and a polarization splitter that is placed after the optical wave plate and extracts the light incident from the optical wave plate as two optical outputs. An optical wavelength meter comprising an element and a logarithmic ratio processing calculation circuit that calculates the ratio of two optical outputs of the polarization separation element.